The present application relates to a communications system and a communication apparatus that build a local area network (LAN) in a building. In particular, the present application relates to a communications system and a communication apparatus that build a LAN easily using a plurality of transmission media.
More specifically, the present application relates to a communications system and a communication apparatus that build a LAN easily in a building using a wireless LAN and power line communication. In particular, the present application relates to a communications system and a communication apparatus that realize high-speed communication by using the wireless LAN and the power line communication at the same time.
Use of an information providing service established on a wide area network, typified by the Internet, has become widespread in recent years, and downloading of large-size data files, distribution of video streams, and so on have become very common. One common mode of enjoying these types of services at home or at other similar places is as follows. A bridge device, such as a router, is connected to a backbone network, such as the Internet, via wired broadband communication, such as asynchronous digital subscriber line (ADSL) or a cable TV. Data is transferred from the bridge device to an information terminal, such as a personal computer (PC), over a LAN built in the home.
FIG. 8 shows an exemplary structure of a communications system for using the Internet at home. A bridge device 103, such as a router, is provided in the home, and the bridge device 103 is connected to a server 101, which is a source of information, via an external network 102, such as the Internet. In addition, a local area network (LAN), such as an Ethernet (registered trademark) network, is built in the home, and a communication terminal 105, such as a PC, is connected to the LAN. The Internet Protocol (IP) is implemented on the communication terminal 105, so that the communication terminal 105 is capable of acquiring data from the server 101 on the Internet to allow the data to be viewed via a browser screen or the like. The IP is described in RFC (Request For Comment)-791 issued by IETF (Internet Engineering Task Force).
In recent years, wireless LANs conforming to IEEE 802.11, for example, have become widespread, and it has become easy to build a LAN in a wireless manner. Accordingly, the bridge device is, as the router, connected to the backbone network, such as the Internet, and functions in the home as an access point for the wireless LAN to provide a service area to a wireless communication terminal. Because the wireless LAN allows flexible Internet connection, the wireless LAN is not simply a substitute for an existing wired LAN but is able to provide a means to connect to the Internet even at public places, such as a hotel, an airport lounge, a station, and a cafe.
FIG. 9 is a schematic diagram illustrating an exemplary structure of a communications system using the wireless LAN. In FIG. 9, a wireless bridge 203 has a network interface (router) function of connecting to a server 201 via a wired transmission path 202, and a function as a wireless LAN access point for a wireless terminal. The wireless bridge 203 acquires data from the server 201 and transfers the acquired data over a wireless transmission path 204. In addition, the wireless bridge 203 has an inter-access point communication function and is capable of connecting to another wireless bridge 205 (or the other wireless bridge 205 operates as a terminal station connected to an access point). The wireless bridge 205 is capable of receiving data via the wireless transmission path 204 and transferring the received data to a communication terminal 207, such as a personal computer (PC), via a wired transmission path 206.
Power line communication (PLC) is another technology for building a network in a building. In the power line communication, a device having a communication function and which accepts supply of power via a power line superimposes a communication signal upon the power line, and communicates with another device having a similar function via the power line.
In the wireless LAN, transmission output is not high because of legal regulations related to radio waves and in order to avoid interference with another system, and thus communication between different rooms may be impossible because of presence of a wall. Meanwhile, in the power line communication, the existing power line is used to realize communication between different devices placed at different rooms provided with AC sockets, and locations of the devices do not pose a problem. The power line communication makes it possible to build the LAN without the need to provide Ethernet (registered trademark) throughout the building, and realize high-speed communication of 100 Mbps or more.
FIG. 10 illustrates an exemplary structure of a communications system in which a part of a wired transmission path between a sever 301 and a communication terminal 307, such as a PC, is replaced with a power-line transmission path 304 by means of a pair of PLC bridge devices 303 and 305. In FIG. 10, the PLC bridge device 303 has a network interface function of connecting to the server 301 via a wired transmission path 302, and a PLC interface function. The PLC bridge device 303 is connected to the other PLC bridge device 305 via the power-line transmission path (i.e., a power line) 304. The PLC bridge device 305 is connected to the communication terminal 307, such as the PC, via a wired transmission path 306.
In the system structure as shown in FIG. 10, communication apparatuses such as the PLC bridge devices need to be placed near the AC sockets. However, when the PLC bridge device is provided with a function of transmitting a signal received via the AC socket to another wireless communication apparatus using a radio signal, the other wireless communication apparatus may be placed at any place (see JP-A-2002-374189, for example).
Here, in general, in wireless communication technologies, systems that use the same frequency channel are easily affected by influence of interference therebetween, a transmission speed is not stable depending on radio wave conditions, and a problem may happen with a traffic that requires high-speed transmission. On the other hand, in the communications system that uses the power line communication, communication behavior varies depending on the structure of a building in which communication is carried out, and communication is easily affected by influence of noises that occur because of everyday actions (such as plugging in and out of a cord, use of a drier, etc.). Thus, in the communications system that uses the power line communication, an ideal transmission speed is not always achieved, and an actual transmission speed may undergo a great reduction depending on noise conditions.
Thus, while the wireless LAN and the power line communication are easy to implement, the), are communications systems that are incapable of stably achieving high-speed communication. Thus, when very high traffic is needed as in high definition transfer, it is very likely that a high enough transmission speed be not achieved thereby.
As such, as a means to allow communication to be performed continuously, methods have been proposed of switching between the wireless LAN and the power line communication to use one of the two transmission media which has the better communication condition (see JP-A-2002-319947 and JP-A-2005-354159). Such communication methods result in improved communication quality, but since only one of the two transmission media is used, the highest possible transmission speed is a maximum transmission speed of one of the two transmission media. Thus, those communication methods also have a problem with stable transmission in high definition transfer or the like.
Further, a method of using the wireless LAN and the power line communication at the same time has been proposed. In this method one packet is divided between a wireless LAN interface and a power line communication interface, and divided parts of the packet are simultaneously transmitted and received, so that an increase in transmission speed is achieved (see JP-A-2006-109022, for example). In this type of communication method, in order to increase the transmission speed, a transmitter divides one packet into parts and adds information about packet division and information about an order of packets to data before transmission, and accordingly, a receiver needs to receive the divided parts of the packet from the respective transmission paths and reconstruct the original data therefrom. That is, in this type of communication method, the transmitter and receiver need be devices having the same mechanism, and this type of communication method has a compatibility problem.